locking/atomic: scripts: fix ${atomic}_dec_if_positive() kerneldoc

  The ${atomic}_dec_if_positive() ops are unlike all the other conditional
atomic ops. Rather than returning a boolean success value, these return
the value that the atomic variable would be updated to, even when no
update is performed.

We missed this when adding kerneldoc comments, and the documentation for
${atomic}_dec_if_positive() erroneously states:

| Return: @true if @v was updated, @false otherwise.

Ideally we'd clean this up by aligning ${atomic}_dec_if_positive() with
the usual atomic op conventions: with ${atomic}_fetch_dec_if_positive()
for those who care about the value of the varaible, and
${atomic}_dec_if_positive() returning a boolean success value.

In the mean time, align the documentation with the current reality.

Fixes: ad8110706f381170 ("locking/atomic: scripts: generate kerneldoc comments")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
---
 include/linux/atomic/atomic-arch-fallback.h | 6 +++---
 include/linux/atomic/atomic-instrumented.h  | 8 ++++----
 include/linux/atomic/atomic-long.h          | 4 ++--
 scripts/atomic/kerneldoc/dec_if_positive    | 2 +-
 4 files changed, 10 insertions(+), 10 deletions(-)
  

On Thu, Jun 15, 2023 at 02:27:34PM +0100, Mark Rutland wrote:
> The ${atomic}_dec_if_positive() ops are unlike all the other conditional
> atomic ops. Rather than returning a boolean success value, these return
> the value that the atomic variable would be updated to, even when no
> update is performed.
> 
> We missed this when adding kerneldoc comments, and the documentation for
> ${atomic}_dec_if_positive() erroneously states:
> 
> | Return: @true if @v was updated, @false otherwise.
> 
> Ideally we'd clean this up by aligning ${atomic}_dec_if_positive() with
> the usual atomic op conventions: with ${atomic}_fetch_dec_if_positive()
> for those who care about the value of the varaible, and
> ${atomic}_dec_if_positive() returning a boolean success value.
> 
> In the mean time, align the documentation with the current reality.
> 
> Fixes: ad8110706f381170 ("locking/atomic: scripts: generate kerneldoc comments")
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Will Deacon <will@kernel.org>

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  include/linux/atomic/atomic-arch-fallback.h | 6 +++---
>  include/linux/atomic/atomic-instrumented.h  | 8 ++++----
>  include/linux/atomic/atomic-long.h          | 4 ++--
>  scripts/atomic/kerneldoc/dec_if_positive    | 2 +-
>  4 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/atomic/atomic-arch-fallback.h b/include/linux/atomic/atomic-arch-fallback.h
> index 8cded57dd7a6f..18f5744dfb5d8 100644
> --- a/include/linux/atomic/atomic-arch-fallback.h
> +++ b/include/linux/atomic/atomic-arch-fallback.h
> @@ -2520,7 +2520,7 @@ raw_atomic_dec_unless_positive(atomic_t *v)
>   *
>   * Safe to use in noinstr code; prefer atomic_dec_if_positive() elsewhere.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline int
>  raw_atomic_dec_if_positive(atomic_t *v)
> @@ -4636,7 +4636,7 @@ raw_atomic64_dec_unless_positive(atomic64_t *v)
>   *
>   * Safe to use in noinstr code; prefer atomic64_dec_if_positive() elsewhere.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline s64
>  raw_atomic64_dec_if_positive(atomic64_t *v)
> @@ -4657,4 +4657,4 @@ raw_atomic64_dec_if_positive(atomic64_t *v)
>  }
>  
>  #endif /* _LINUX_ATOMIC_FALLBACK_H */
> -// 3916f02c038baa3f5190d275f68b9211667fcc9d
> +// 202b45c7db600ce36198eb1f1fc2c2d5268ace2d
> diff --git a/include/linux/atomic/atomic-instrumented.h b/include/linux/atomic/atomic-instrumented.h
> index ebfc795f921b9..d401b406ef7c4 100644
> --- a/include/linux/atomic/atomic-instrumented.h
> +++ b/include/linux/atomic/atomic-instrumented.h
> @@ -1570,7 +1570,7 @@ atomic_dec_unless_positive(atomic_t *v)
>   *
>   * Unsafe to use in noinstr code; use raw_atomic_dec_if_positive() there.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline int
>  atomic_dec_if_positive(atomic_t *v)
> @@ -3134,7 +3134,7 @@ atomic64_dec_unless_positive(atomic64_t *v)
>   *
>   * Unsafe to use in noinstr code; use raw_atomic64_dec_if_positive() there.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline s64
>  atomic64_dec_if_positive(atomic64_t *v)
> @@ -4698,7 +4698,7 @@ atomic_long_dec_unless_positive(atomic_long_t *v)
>   *
>   * Unsafe to use in noinstr code; use raw_atomic_long_dec_if_positive() there.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline long
>  atomic_long_dec_if_positive(atomic_long_t *v)
> @@ -5000,4 +5000,4 @@ atomic_long_dec_if_positive(atomic_long_t *v)
>  
>  
>  #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
> -// 06cec02e676a484857aee38b0071a1d846ec9457
> +// 1568f875fef72097413caab8339120c065a39aa4
> diff --git a/include/linux/atomic/atomic-long.h b/include/linux/atomic/atomic-long.h
> index f6df2adadf997..c82947170ddc8 100644
> --- a/include/linux/atomic/atomic-long.h
> +++ b/include/linux/atomic/atomic-long.h
> @@ -1782,7 +1782,7 @@ raw_atomic_long_dec_unless_positive(atomic_long_t *v)
>   *
>   * Safe to use in noinstr code; prefer atomic_long_dec_if_positive() elsewhere.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline long
>  raw_atomic_long_dec_if_positive(atomic_long_t *v)
> @@ -1795,4 +1795,4 @@ raw_atomic_long_dec_if_positive(atomic_long_t *v)
>  }
>  
>  #endif /* _LINUX_ATOMIC_LONG_H */
> -// 029d2e3a493086671e874a4c2e0e42084be42403
> +// 4ef23f98c73cff96d239896175fd26b10b88899e
> diff --git a/scripts/atomic/kerneldoc/dec_if_positive b/scripts/atomic/kerneldoc/dec_if_positive
> index 7c742866fb6b6..04f1aed3cf830 100644
> --- a/scripts/atomic/kerneldoc/dec_if_positive
> +++ b/scripts/atomic/kerneldoc/dec_if_positive
> @@ -7,6 +7,6 @@ cat <<EOF
>   *
>   * ${desc_noinstr}
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  EOF
> -- 
> 2.30.2
>